But it's too early to tell and some details don't quite add up - in a recent interview commander of the Space Forces said that the radar is being built "at a mountain with the height of 400 m." Google Earth doesn't show any mountains at this location.

That's a good question. And, frankly, I don't have a good answer. I find it hard to believe that Russia did not see the missile, but I find it equally hard to understand why Russia said it wasn't an ICBM.